Fluid-Flow Rotator Based on Hydrodynamic Metamaterial

Metamaterials are rationally designed periodic micro- or nanostructures that do not exist in nature. Recently, metamaterials for hydrodynamic phenomena have attracted immense attention from scientists, demonstrating magical fluid manipulation. Here we report a passively operating hydrodynamic metamaterial rotator that allows control of the flow direction without application of external forces and fluidic properties. Viscosity tensors to model the rotators for virtually twisting fluidic coordinate systems are derived on the basis of transformation hydrodynamics and are subjected to numerical simulations to predict the pressure and velocity fields. A microstructured rotating metamaterial is designed and produced in a microfluidic device. The hydrodynamic rotation of flowing water is experimentally confirmed, demonstrating the artificial manipulation of the flow direction.